System and method for reducing hydrocarbons in wastewater

ABSTRACT

A system and method for reducing hydrocarbons in wastewater includes an oil separator and a stripper tower. The tower has a housing that includes a stripper section and a condensation section. The stripper section includes a plurality of trays and steam inlet under the trays. The condensation section includes a plurality of trays and a pan tray having provisions to allow vapors to rise from the stripper section. The method includes having the oil separator remove the soluble oil from the wastewater stream which passes through the stripper section and has steam remove the hydrocarbons. The resulting vapors then contact cold process fluid which results in a heated process fluid stream. A portion of this heated process fluid stream is then mixed with crude so that hydrocarbons can be assimilated into the crude.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a system and method for reducing hydrocarbonsin wastewater, and in particular, benzene in desalter effluent water andcontaminated ground water.

2. Background Art

Government agencies are providing guidelines of how hazardous wastesshall be disposed of and limits to the amount of hazardous wastes thatmay be released to the atmosphere. The Environmental Protection Agencyhas prepared a regulation, entitled "National Emission Standards forHazardous Air Pollutants" (NESHAPS), that provides that refinerywastewater shall have the benzene count reduced before it is releasedfrom the refinery. Desalter effluent water and other water streams ofmany refineries have benzene counts far in excess of the regulationlimit.

The desalter effluent water is used to interact with crude oil in one ormore stages to remove salts from the crude oil. This water-oilinteraction results in benzene and other hydrocarbons becoming part ofthe desalter effluent water composition and raising the benzene levelabove the allowable regulation limits. The ground water around and undera refinery may be contaminated with benzene and other hydrocarbons fromoil spills and leakages within the refinery facilities. This groundwater also can have a benzene count that exceeds the allowable limit.

With this regulation in effect, refineries may no longer just dump theirdesalter effluent water or other hydrocarbon-contamined water streams.If the refineries do so, they face stiff fines and penalties as setforth in the NESHAPS regulation for harming the environment.

SUMMARY OF THE INVENTION

In accordance with the present invention, hydrocarbons can be reduced ina wastewater stream by a system having an oil separator and a strippertower. The tower has a housing having a stripper section that includes aplurality of trays and a steam inlet located below the stripper trays,and a condensation section located in the upper half of the housinghaving a plurality of trays and a pan tray located below thecondensation trays.

The system has the wastewater stream pass through the oil separator andenter just above the stripper section to pour over the stripper traysand meet head-on steam from the steam inlet to remove hydrocarbons fromthe wastewater stream. The hydrocarbon is carried as vapor up into andthrough the condensation section where the vapors encounter a coldprocess fluid stream that carries away hydrocarbons back to a desalterstage to assimilate the hydrocarbons into crude being processed.

In accordance with another aspect of the present invention, there isprovided a method for reducing hydrocarbons in a wastewater stream byremoving insoluble oil, contacting the wastewater stream with steam toremove hydrocarbons, contacting the resulting vapors with a cold processfluid to condense hydrocarbons into the heated process fluid stream.This heated fluid stream is mixed with crude so that hydrocarbons can beassimilated into the crude.

Objects, features and advantages of this invention are to provide asystem and method that can reduce hydrocarbons in a wastewater streamefficiently and effectively through a simplified and economical design,manufacture and assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be apparent from the following description, appendedclaims and accompanying drawings in which:

FIG. 1 is a schematic diagram of an improved hydrocarbon-reducing systemfor wastewater of the present invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

With specific reference to FIG. 1, a diagram illustrates a hydrocarbon(in particular, benzene) reducing system 10 interconnected to awastewater stream pipeline 12 that receives desalter effluent water frompipeline 14 and/or other contaminated water streams such as contaminatedground water from pipeline 16.

The benzene-reducing system 10 has two main sections: an oil separator20 and a hydrocarbon stripper tower 22. Preferably, the oil separator 20has a hydrocyclone 24 and an oily water separator drum 26 connected byconduit 28 to the stream exit of the hydrocyclone 24.

The hydrocarbon stripper tower 22 is made up of a column housing 32having a stripper section 34 located in its lower portion and acondensation section 36 located in the upper portion of the columnhousing 32. The stripper section 34 includes a number of spaced-aparttrays 40 (preferably eleven) and a steam inlet 42 located below thesetrays 40.

The condensing section 36 includes several trays 44, with the preferredembodiment having four stacked one on top of the other. Located belowthese is a pan tray 46, with chimney risers to allow vapors to pass fromthe stripper section 34 into and through the condensation section 36.

The column housing 32 has several openings through its perimeter, onelocated above the stripper section 34 to accommodate the wastewater feedline 50 and another opening to accommodate cold process fluid stream inline 52. Out of the top of the column housing 32 is a line 54 that leadsto a low pressure gas system. Out of the bottom of the column housing 32is a pump-out line 58 that directs the treated wastewater stream to aheat exchanger 56.

In operation, the benzene-reducing system 10 is used in a process of thepresent invention, as now will be described. Desalter effluent water inline 14 is received hot from the desalter stage 60. Contaminated waterfrom tank 62 is received through line 16 and is heated in heat exchanger56. The total wastewater stream is carried by line 12 into the oilseparator 20.

In the preferred embodiment, the wastewater stream is fed into first ahydrocyclone 24 that uses fluid momentum intensity effects to removeand/or coalesce insoluble oil droplets in the wastewater stream. Anyremaining insoluble oil droplets in the wastewater stream is separatedby oil/water separator drum 26. These operations may be reversed. Thewastewater stream, less any insoluble oil, is deposited into thehydrocarbon stripper 22 via line 50. The wastewater stream is spilledover the eleven trays 40 and is met from the bottom up by a strippingstream from the steam inlet 42. This steam strips the benzene and otherhydrocarbons from the wastewater stream and proceeds up and through thecondensing section 36. The wastewater stream that has passed over theeleven trays 40 and reaches the bottom of the column housing 32 free ofbenzene and other soluble hydrocarbons. This treated wastewater streamis drained through an outlet into pump-out line 58 and directed to heatexchanger 56 to heat the contaminated water stream before it enters theoil separator 20. This operation reduces the amount of steam necessaryfor hydrocarbon stripping.

The vapors carrying the hydrocarbon pass through the chimney risers ofthe pan tray 46 and up through the four trays 44. Cold process fluid isintroduced through line 52 and contacts the vapors and condenses thehydrocarbons, as well as the steam, into the cold process fluid. Part ofthis cold process fluid is fresh makeup water from line 72. This fluidproceeds down and through the trays onto the pan tray 46. The pan tray46 is the total draw tray; it removes all of the now heated processfluid stream ladened with condensed hydrocarbons out to line 64. Thisheated stream is split up wherein a portion is directed into a line 66that passes through a cooler 68 and becomes a chilled process fluidstream in line 74. This stream is mixed with fresh makeup water fromline 72 to become cold process fluid for further condensation purposes.

The remaining portion of the heated process stream is diverted to line70 to be mixed with the crude in line 76. Because of the equilibriumconditions in the desalter stage 60, the heated process fluid streampasses benzene and other hydrocarbons to the crude to be processed withthe bulk of the benzene from the crude in the normal refinery processingflow. An advantage of this hydrocarbon-reducing system is that thehydrocarbon-laden process water is heated by the steam vapor andeliminates the need for heating desalter makeup water, resulting in fuelsavings at the crude heater.

This system and process reduces benzene in wastewater streams, meetingthe environmental regulations set down by the Environmental ProtectionAgency. Also, this system reduces energy costs by providing heatedprocess fluid stream to be mixed with the crude, saving fuel at thecrude heater. Additional energy savings are realized by heating thecontaminated water stream before the hydrocarbon stripper tower, becauseless steam is necessary for stripping.

It is to be understood that the terminology, as employed in thedescription and claims incorporated herein, is used by way ofdescription and not by way of limitation to facilitate understanding ofthe structure, function and operation of the combination of elementswhich constitute the present invention. Moreover, while the foregoingdescription and drawings illustrate in detail working embodiments of theinvention, to those skilled in the art to which the present inventionrelates, the present disclosure will suggest many modifications inconstruction, as well as widely differing embodiments and applicationswithout thereby departing from the spirit and scope of the invention.The present invention, therefore, is intended to be limited only by thescope of the appended claims in the applicable prior art.

What is claimed is:
 1. A process for reducing benzene in desaltereffluent water comprising the steps of:a. removing insoluble oil fromthe desalter effluent water; b. contacting the desalter effluent waterwith steam to remove benzene from the desalter effluent water to producevapors containing hydrocarbons; c. contacting said vapors containinghydrocarbons with a cold process fluid stream; d. condensing vaporscontaining hydrocarbon into the cold process fluid stream which resultsin a heated process fluid stream; e. mixing a portion of the heatedprocess fluid stream with crude oil to deposit hydrocarbons into thecrude oil; f. cooling a remaining portion of the heated process fluidstream to create a chilled fluid stream; and g. mixing the chilledprocess fluid stream with fresh makeup water to create the cold processfluid stream to condense additional vapors containing hydrocarbons.